What it is
The plug can be made of crystals, mucus and inflammatory cells, and sometimes a small stone or a spasm of the urethra's muscle is to blame. A male cat's urethra is especially long and narrow, so this happens mainly to males, although females are not completely safe.
When urine cannot drain, the bladder keeps filling and stretching, and substances the kidneys should remove build up in the blood, potassium among them. Too much potassium upsets the heart, so the cat's condition can get worse very quickly.
It is easy to mistake this for constipation, because the cat squats and strains in much the same way. Do not guess and do not wait for morning: straining in the litter box with no urine coming out is a reason to go to a vet straight away.
Signs you may notice
- Squats in the box but no urine comes
- Cries or yowls while trying to urinate
- Licks its genitals persistently
- Vomits
- Hides and turns listless
- Hunches, avoids being touched
A cat squats in the litter box again and again and strains, but no urine comes, or only a drop; it may cry out, lick itself persistently and vomit. Soon it hides, turns listless and avoids having its belly touched.
When to see a vet
A cat that strains and passes no urine needs a vet immediately, day or night. Do not wait for it to pass and do not try anything at home.
This is general information, not veterinary advice. For your own cat's health, tests and treatment, see a vet.